In many fluid handling applications such as, for example, the pumping of coating material in a system for coating the interior of can bodies, it is important to maintain isolation of the material or delivery medium being pumped from the lubricant used in the pumping apparatus. Contamination of the lubricant by the pumped material may cause damage to the pump. Moreover, mixing of lubricant from the pump with the pumped material can impair the properties of the pumped material. Thus in a can coating system, contamination of the coating material by the lubricant may render the coating material toxic or otherwise impair proper functioning of the coating.
In the past, a diaphragm type pump has been used to avoid mixing of any lubricant with a delivery medium being pumped. In such diaphragm pumps, one or more flexible diaphragms serve as fluid barriers as well as mechanical couplings between a lubricated drive assembly and a pumping chamber. Typically, the drive assembly supplies a motive force which is transferred through the diaphragm to the delivery medium contained in a pumping chamber. The pumping chamber includes an inlet, an outlet and respective associated valve assemblies for controlling the flow of the pumped fluid to and from the pumping chamber.
One example of such a diaphragm pump is illustrated in Wanner U.S. Pat. No. 3,775,030, the disclosure of which is expressly incorporated herein by reference in its entirety to form part of this application. The Wanner patent discloses a diaphragm pump having three identical sets of single diaphragms disposed at 120 degree intervals for sequential actuation by respective associated piston assemblies, each of which is reciprocably driven by a rotatably driven cam plate. The pistons and cam plate form part of the drive assembly which is bathed in hydraulic pumping and lubricating fluid. As the pistons reciprocate, they flex the diaphragms to pump fluid material in the pumping chamber from an inlet to an outlet through respective valve assemblies. The hydraulic lubricating or pumping fluid is separated from the fluid material being pumped in the pumping chamber by only the single diaphragms. Thus, if any of the three diaphragms should rupture, undesired mixing of hydraulic fluid with the material being pumped would occur. Since the pump includes no means to detect such mixing, that adverse condition would be likely to persist for some period of time, perhaps worsening, before being detected so that appropriate corrective action could be initiated.
One possible solution to these problems is proposed in U.S. Pat. No. 3,131,638 wherein each diaphragm device comprises three or more diaphragms arranged in superposed layers. Failure of a single diaphragm will not result in mixing of lubricant and the delivery medium. Moreover, any rupture and leakage through one of the outer two diaphragms is monitored. Particularly, one of the center diaphragms is perforated with radial slots communicating with the environment. Leaking material is transmitted outwardly therethrough into a leak indicating device. This allows monitoring any leakage of hydraulic fluid or the delivery medium being pumped to indicate failure of one of the outer diaphragms.
In another diaphragm pump assembly, as shown in U.S. Pat. No. 3,605,566, the space between dual diaphragms is filled with a hydraulic medium supplied from a tank. If a diaphragm ruptures, either hydraulic fluid or delivery medium flows into the tank where its presence can be sensed by means of noting the increased tank volume.
Because the contaminating fluid in each of these devices must make its way into a tank some distance from the leak and because the sensible concentration of the contaminant is diluted by the volume of hydraulic medium in the tank, sensing a rupture may be unduly delayed. Also, the tank and necessary piping connections are bulky and cumbersome to assemble and maintain.
Another device to monitor rupture of one of two diaphragms, and resultant fluid leakage, is disclosed in U.S. Pat. No. 3,431,823. The space between a pair of diaphragms is filled with a buffer fluid which hydraulically couples the two diaphragms together, eliminating one lifting off from the other. If the buffer fluid is contaminated by either pumped material or pumping fluids, its pH is changed. This change is sensed by an electrode disposed in the fluid filled region between the diaphragms.
Despite these attempts, problems still exist in dual diaphragm pumps. Detection of leakage can be delayed. Moreover, the sensing of a pH change may require an increased concentration of contaminant in the buffer fluid before a leak signal can be generated. This could permit, in the case of rupture of the diaphragm on the pumped material side, at least leakage of the buffer material into the pumped fluid without detection for some time.
In another aspect of such pumps, the assembly of the dual diaphragms is complicated. Such a combined diaphragm device might typically include both diaphragms, intermediate spacers, and the "buffer" fluid. It is difficult to hold these parts together during assembly without losing the buffer fluid.
One attempted solution to this difficulty is discussed in U.S. Pat. No. 3,431,823. The diaphragm assembly comprises a structural unit wherein each diaphragm is initially clamped between an inner support and one of a pair of clamping rings so that the unit may be filled with buffer fluid prior to assembly. Once the unit is assembled into a pump, the pump casing clamps the diaphragms at a point radially inwardly of the point held by the clamping rings. Thus, the clamping rings do not get in the way of the pump casing faces. After assembly, the clamping rings serve no significant purpose.
Accordingly, it has been one objective of the invention to provide an improved, sensitive, quick-acting leak or diaphragm rupture detection apparatus.
It has been a further objective of the invention to provide an improved dual diaphragm apparatus facilitating diaphragm to pump assembly, and the scheduled or emergency replacement of the diaphragm apparatus without loss of buffer fluid.